Injection heads are known for directly injecting treatment substances into eggs, such as vaccines, antibiotics or vitamins, in order to limit the mortality rate or increase the growth of the embryos. Such injection heads conventionally comprise a plurality of injectors able to move vertically above a conveyor conveying eggs to be treated, the eggs conventionally being placed in alveoli in so-called incubation trays.
There has been proposed, in particular in the patent document FR 2 873 894, an injection head in which each injector is equipped with its own movement means for moving the injector from a raised position to an injection position in which its needle can inject a substance into the egg. The injection head comprises a fixed injector support intended to be disposed above eggs to be treated, and injectors mounted on said injector support, each injector comprising an injection body, an injection needle mounted on said injection body and communicating with an inlet of said body for its supply with at least one substance to be injected, and individual movement means, such as a pneumatic actuator, by means of which the injector is connected to said injector support, said movement means being able to move said injection body between a raised position and an injection position. During the movement towards the injection position, the needle pierces the shell of the egg. After having pierced the shell, the needle pierces the shell membrane in order to inject a treatment substance into the amniotic fluid or directly into the embryo.
Between two injection cycles, the injector must be disinfected to prevent any contamination from one egg to another. One of the advantages of this type of injector, in which the needle serves both to pierce the shell and to inject the substance, is that it can easily and effectively be disinfected between two injection cycles. The pressure of the pneumatic actuator, which defines the penetration force of the needle, does, however, prove to be particularly tricky to adjust. This is because the pressure must be sufficient to pierce the shell, in particular to prevent the needle ricocheting on the shell. If the pressure is too high, the needle may break the eggshell and/or pierce the shell membrane or the embryo too violently, which may cause irreversible trauma to the embryo. In addition, the travel of the actuator is relatively long in order to be able to pierce the shell and then the shell membrane, and the rod of the actuator can have a tendency to twist.
To resolve these problems partly, it was proposed in the patent document FR 2 838 920 to inject the treatment substance under pressure from the air pocket of the egg so that the substance reaches the amniotic fluid after having passed by pressure through the shell membrane. This solution is, however, not applicable for the injection of substances, in particular vaccines, that do not withstand pressurization.
There are also known injection heads in which the injectors comprises a punch in which the needle is mounted slidably, the punch firstly being lowered to pierce the shell, and then the needle is lowered to inject the substance. The punch and needle system of this type of injector does, however, can be very difficult to clean.